1. Field of the Invention
The present invention relates to systems having non-linear characteristics such as gamma characteristics, and more particularly, to an apparatus and method for converting input data so that a system having a non-linear response generates output that is linearly related to the input data.
2. Description of the Related Art
In general, many systems exhibit some type of non-linear characteristics or responses. Particularly, many home appliances, computers, and communication systems, which are familiar in our daily life, have non-linear characteristics. For example, t display device, such as a cathode ray tube (CRT) in a television (TV) or a computer monitor, or a charge coupled device (CCD) in a camera, shows a gamma intensity distribution caused by non-linearity of phosphorescence in the device. In a CRT, the gamma characteristics cause output brightness to have a non-linear relationship with an input luminance signal. This can distort the image on the CRT if the input signal is generated under the assumption of a linear response. Thus, it is necessary to apply gamma correction such input signals to ensure a linear relationship between the input signal and the output luminance.
FIG. 1 is a graph illustrating gamma correction for a CRT of a TV. Here, the X-axis represents the normalized voltage of a video signal input to the CRT, and the Y-axis represents the normalized intensity of the light emitted from the CRT. If the input voltage of the CRT and the intensity of the emitted light are normalized, the CRT has non-linear characteristics 14 as shown in FIG. 1. According to the CRT characteristics, the CRT response is weak for a small input signal and stronger when a large input signal. The intensity (Y) of the emitted light with respect to the input voltage (X) to the CRT is expressed exponentially as in Equation 1. EQU Y=X.sup.2.2 Equation 1
If a gamma-corrected signal 10, which is obtained by gamma-correcting a linear video signal 12, is input, the CRT emits the light having intensity proportional to the original video signal 12.
A gamma correction apparatus is required when the data to be input to a display device requires compensation for the gamma characteristics of the display device. A conventional gamma correction apparatus uses a look up table stored in a memory such as a RAM or ROM. Here, the look up table contains gamma corrected values previously stored at addresses corresponding to the associated input values, and in place of each input digital value, the look up table outputs to the display device the gamma corrected value read using the input digital value as a memory address.
Look up tables for gamma correction become larger as the range of input data values increases. For example, a look up table for a conventional gamma correction apparatus that corrects an N-bit digital input signal is 2.sup.N, W, where 2.sup.N is the depth of the look up table and W is the width of the look up table. Larger look up tables make integration more difficult and increases system costs. In addition, a programmable system for gamma correction typically uses RAM such as SRAM or DRAM for the look up table, instead of ROM. However, RAM is typically more complicated and larger than ROM, making look up table size even more critical in programmable systems.